The present invention relates to a structural body and to a method of manufacturing the structural body. For example, the present invention is directed to a structural body and a manufacturing method in which a structural body is formed by joining extruded frame members made of an aluminum alloy, such as are used in a railway vehicle or a building structure.
Friction stir welding is a method in which, by rotating a round rod (called a xe2x80x9crotary toolxe2x80x9d) which is inserted into a joint between members to be joined and moving the rotary tool along a welding line of the extruded frame members, the joint is exothermally heated, softened and plastically fluidized, so that a solid-state welding is carried out.
The rotary tool is comprised of a small diameter portion, which is inserted into the welding joint, and a large diameter portion, which is positioned outside of the small diameter portion of the rotary tool, the small diameter portion and the large diameter portion of the rotary tool having the same axis of rotation. A boundary between the small diameter portion and the large diameter portion of the rotary tool is inserted slightly into the welding joint during welding. The above-stated technique is disclosed, for example, in Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2). In FIG. 9 of this document, a joining of two faces of a pair of hollow extruded frame members is carried out from one of the two faces of the hollow extruded frame members. Further, a coupling member for preventing a deformation of the hollow extruded frame member is shown.
The main difference between friction stir welding and arc welding resides in the fact that, in friction stir welding which involves insertion of a rotary tool into a narrow gap between members to be subjected to welding, a large load is applied to the members being welded. This load acts mainly in the insertion direction (an axial center direction) of the rotary tool. Namely, the insertion force of the tool acts on the members to be subjected to welding. When the hollow extruded frame members are subjected to friction stir welding, the insertion force acts against a rib which connects two parallel face plates, with the result that the hollow extruded frame member may be deformed. For these reasons, it is necessary to form a structure in which a deformation of the coupling member portion can be prevented.
An example of deformation prevention means is disclosed in Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2). In this document, to a joining portion of the two hollow extruded frame members, a vertical plate (called a xe2x80x9clengthwise ribxe2x80x9d) for joining two face plates of the hollow extruded frame member is provided. This lengthwise rib is positioned on an extension line of an axial center of the rotary tool. The lengthwise rib is one to which two face plates of the hollow extruded frame member are connected. Since a large load acts concentrically on the lengthwise rib, it is necessary to increase the plate thickness of the hollow extruded frame member. For this reason, there is a difficulty in obtaining a light weight structural coupling member.
Further, this lengthwise rib of the hollow extruded frame member can be considered from another aspect. When an outside bending force acts on the hollow extruded frame member, it is well known that the whole rigidity performance dominated by the rib. To improve the rigidity performance relative to the outside bending force, it is desirable to arrange the rib to have a consistent forty five degree angle relative to the face plate, which is a main stress force perpendicular to a shearing force. However, a lengthwise rib which is perpendicular to the two face plates of the extruded member hardly contributes to the strengthening of the member.
As stated above, regardless of the fact that the lengthwise rib hardly contributes to an improvement of the rigidity performance when the structural body is used as a strengthening member, since this lengthwise rib is necessary to increase the plate thickness of the hollow extruded frame member so as to support the insertion force during friction stir welding, it makes it difficult to achieve a light weight structure of the coupling member of the hollow extruded frame member.
An object of the present invention is to provide a structural body having a light weight structure and a high rigidity performance, and a method of manufacturing the structural body.
The above-stated object can be attained by a manufacturing method comprising the steps of: preparing two hollow frame members in which two sheet face plates are connected with a truss-shaped structure by plural ribs, an end portion of one of the face plates is positioned in the vicinity of an apex of the truss structure, and an end portion of another of the face plates has a projection extending toward the end portion of the one of the face plates; welding the projected face plates to each other from a side of the one of the face plates; arranging a connection member between the end portion of the one of the face plates of one of the two hollow frame members and the end portion of the one of the face plates of the other of the two hollow frame members; and welding the respective end portions of the connection member to the respective face plates.
The above-stated object can be attained by a manufacturing method comprising the steps of: connecting two face plates of two hollow frame members by plural ribs, and arranging the two hollow frame members so that an end portion of one of the two face plates of one frame member is projected from an end portion of one of the two face plates of the other frame member; welding the projected members to each other from above the two face plates using friction stir welding; and overlapping the respective end portions of one connection member to a connection portion which is formed at one end portion and the rib of the other of the two face plates of said one of the two hollow frame members and to a connection which is formed at one of the end portion and the rib of the other of the two face plates of the other of the two hollow frame members; welding of the one of the two hollow frame members and one end of the connection member at the overlapped portion is carried out from an outer side of the hollow frame member using friction stir welding and the position of the friction stir welding is an inner side position which has a portion not being subjected to the friction stir welding to one end of the connection member; and in a welding of the other of the two frame members and the other end of the connection member at the overlapped portion is carried out from an outer side of the hollow frame member using friction stir welding or the other end of the connection member and the other of the two face plates of the hollow frame member are joined by arc welding, and the position of the friction stir welding is an inner side position which has a portion not subjected to friction stir welding to one end of the connection member.
The above-stated object can be attained by a friction stir welding method comprising the steps of: overlapping one end portion of a first member and one end portion of a second member, the overlapped portion is positioned between another end portion of the first member and another end portion of the second member; and in a state in which a rotary tool is inclined relative to the overlapped portion, the rotary to is inserted into the first member and the second member to carry out a friction stir welding.